Final answer:
Records of food purchases by operators should be kept for at least 90 days according to the U.S. FDA's Food Code to ensure traceability in the event of a foodborne illness or recall.
Step-by-step explanation:
The question pertains to the duration of record keeping for the purchase of foods by operators. The recommended length of time to keep these records is determined by regulatory agencies such as the Food and Drug Administration (FDA) or local health departments. Based on the U.S. FDA's Food Code, it is recommended that food establishment operators keep records of food purchases for a minimum of 90 days from the date of purchase. This ensures that there is sufficient information available in the event of a foodborne illness investigation or a recall of food products.